1. Field of the Invention
The present invention relates to a sheet processing apparatus having folding means for folding a sheet on which an image was formed, and an image forming apparatus having such a sheet processing apparatus. More specifically, the present invention relates to a sheet processing apparatus which can be made compact and can prevent damage of a sheet, and an image forming apparatus having such a sheet processing apparatus.
2. Related Background Art
Conventionally, regarding image forming apparatuses such as copiers, printing machines, laser beam printers and the like, there has been proposed a sheet processing apparatus in which, for example, after sheets on which images were formed and discharged from a main body of the image forming apparatus are successively received, the sheets are conveyed to folding means, where double-folding processing is carried out, and, thereafter, the sheets are discharged onto a sheet stacking portion (refer to Japanese Patent Application Laid-open No. 2001-26359).
FIG. 5 is a schematic constructional view of a conventional sheet processing apparatus having such a construction. As shown in FIG. 5, a sheet processing apparatus 1000 includes conveying rollers 203, a sheet stopper 205, a stapler 206, a thrusting plate (folding means)209, a pair of folding rollers 208, sheet discharging rollers 210 and a stacking tray (sheetstack stacking means) 211, in order to perform such folding processing.
Here, in the sheet processing apparatus 1000, a sheet discharged from a main body of an image forming apparatus (not shown) and conveyed into the sheet processing apparatus is firstly conveyed by the conveying rollers 203 until a leading end of the sheet reaches the sheet stopper 205, and, thereafter, lateral sides of the sheet reached to the sheet stopper 205 are aligned by sheet aligning means (not shown).
By repeating such operations with respect to a plurality of sheets, the plurality of sheets are stacked on the sheet stopper 205 and, then, stapling processing is performed by the stapler 206. Thereafter, by thrusting the thrusting plate 209 toward a central portion of the stacked sheets, the sheet stack is advanced into a nip of the folding roller pair 208, so that the sheet stack is double-folded by the folding roller pair 208. Thereafter, the double-folded sheet stack is discharged by the sheet discharging rollers 210 onto the stacking tray 211 through a stack discharging outlet 611 provided at a lower part of a main body 1001 of the sheet processing apparatus.
By the way, in a case where the sheet stack so double-folded is discharged onto the stacking tray 211, since the sheet stack is swollen upwardly in a folded portion at a discharging side end, if a plurality of sheet stacks are stacked on the stacking tray 211, a discharging downstream side of the sheet stacked on the stacking tray 211 will be swollen upwardly.
If the discharging sides of the sheet stacks are swollen in this way, since subsequent discharging of the sheet stack onto the stacking tray cannot be performed properly, as shown in FIG. 5, a pressing member 212 for pressing the discharging downstream sides of the sheet stacks is provided above the stacking tray 211 for a rotational movement around a fulcrum 216.
On the other hand, in FIG. 5, there are also provided a sample tray 701 on which sheets passed through a non-sort path 521 after conveyed from the main body of the image forming apparatus (not shown) are stacked, and a stack tray 700 on which sheets after passed through a sort path 522 and subjected to aligning processing, if necessary, and stapling processing effected by a stapler 601 are discharged.
By the way, the stack tray 700 can be moved in an up-and-down direction so that, as a sheet stacking amount is increased, the stack tray is shifted downwardly. When the stack tray 700 is shifted downwardly to pass by the stack discharging outlet 611, the sheets stacked on the stack tray 700 may enter into the stack discharging outlet 611.
To avoid this, in the past, the main body 1001 of the sheet processing apparatus is provided with a shutter member 613 for opening and closing the stack discharging outlet 611 so that, when the stack tray 700 is lowered, by lowering the shutter member 613 together with the stack tray 700, the stack discharging outlet 611 is closed. By closing the stack discharging outlet 611 upon lowering of the stack tray 700, the sheets stacked on the stack tray 700 are prevented from entering into the stack discharging outlet 611.
Incidentally, the shutter member 613 is biased upwardly by an extension spring 615 so that the shutter member 613 is normally held at a position for opening the stack discharging outlet 611 and, when the stack tray 700 is lifted, the shutter member is lifted by following the stack tray 700, thereby opening the stack discharging outlet 611.
However, in the conventional sheet processing apparatus having the above-mentioned shutter member 613 and pressing member 212 and an image forming apparatus having such a sheet processing apparatus, in a case where the pressing member 212 is protruded from the stack discharging outlet 611 out of the main body 1001 of the sheet processing apparatus, since the pressing member 212 constitutes an obstruction, the shutter member 613 cannot be lowered adequately. To avoid this, as shown in FIG. 5, the pressing member 212 is provided within the main body 1001 of the sheet processing apparatus.
However, in a case where the pressing member 212 is provided within the main body 1001 of the sheet processing apparatus in this way, a lateral dimension of the main body 1001 of the sheet processing apparatus is increased, which makes the sheet processing apparatus 1000 bulky, with the result that the image forming apparatus having the sheet processing apparatus 1000 is also made bulky. Further, in the case where the pressing member 212 is disposed within the apparatus, the sheet stacks to be discharged and stacked also remain within the apparatus, which causes a problem that it is difficult to take out the sheet stack.
On the other hand, in the case where the pressing member 212 is provided within the main body 1001 of the sheet processing apparatus, although the shutter member 613 can be lowered adequately, if the shutter member 613 is lowered too great, the sheet stack may be pinched between the shutter member and the stacking tray 211. If the sheet stack is so pinched, the sheet stack may be damaged.